Ultrasound imaging devices are widely used because they are non-destructive, radiationless, and highly flexible in operation. Conventional ultrasound imaging devices provide only two-dimensional images of the human body. Therefore, the sizes and shapes of lesions can only be empirically estimated by doctors based on a plurality of two-dimensional images, and the three-dimensional geometry of a lesions and its surrounding tissues must be imagined by the doctor. This leads to difficulties in diagnosis.
With the application of 3D visualization technology in ultrasound imaging systems, diagnosis has become more convenient. For example, a 3D image may be reconstructed base on a series of two-dimensional images and then may be displayed on a monitor. Not only the overall visual construction of the imaging object may be obtained from the 3D image, but also a lot of important 3D information may be saved. As a result, 3D ultrasound imaging devices have been widely used in clinical practice in recent years.
The 3D ultrasound imaging process usually includes three steps: data acquisition, reconstruction and rendering. 3D ultrasound volume data are collected in the data acquisition step. In the reconstruction step, the collected volume data are converted to corresponding volume data in Cartesian coordinates. To obtain an accurate and undistorted 3D image, the relative position of the volume data in Cartesian coordinates must be consistent with the real space position of the volume data. In the rendering step, the volume data are calculated using a visualization algorithm to obtain visual data, after which the visual data are displayed on a monitor.
In order to obtain more effective 3D rendering, 3D ultrasound systems typically use VOI (volume of interest) technology. The VOI represents a user-configurable geometric figure in three-dimensional space. Using the VOI in 3D rendering, only the volume data inside the geometric figure are used to produce a 3D image. The volume data in which users are interested are defined as the target, while the other data are defined as the background. If the users can make the target into the VOI, then only the 3D image of the target is obtained and displayed. Thus, VOI technology facilitates target observation.
Traditional VOI is preset as a rectangular parallelepiped that includes 6 flat surfaces. This can easily lead to ineffectiveness of separating the target and the background when the target profile is complicated. If at least one of the flat surfaces is replaced by a “curved” surface, it is referred to as a curved surface VOI. The curved surface VOI greatly increases the flexibility of the VOI setting, making it easier for users to separate the target and background based on objective conditions or subjective personal ideas.
U.S. Pat. No. 7,433,504 discloses a method for defining a volume of interest in a medical image. According to this method, a user interface is used to select a point on an initial linear border segment of a VOI. The user then moves the point from its initial position on the linear border segment to a new position and a processor then forms a new, non-linear border segment that includes the point. A 3-D presentation of the VOI is then created.